The present invention relates to display devices and, more specifically, to flat panel display devices that are driven by external control signals.
Conventional flat panel image display devices such as liquid crystal and LED display devices are controlled through the use of some interface, either analog or digital. In digital-processor based systems, these devices are then driven by digital/analog hybrid devices that drive the display and receive digital control signals from external computing devices. Additionally, image data must typically be buffered in some external memory device or devices.
FIG. 1 shows a typical LED display device 200 that includes a grid of row 202 and column 204 addressing lines. A light emitting diode 206 is located at the juncture of each row and column addressing line. Pixel driver circuitry includes a column shift register 208 and a row shift register 210, and row and column drive amplifiers 212 and 214. In operation, image data and control signals are delivered to the row and column shift registers to control the drive amplifiers to produce an image on the display. LCD panels and other flat-panel display technologies employ similar device structures, where the pixel site light emitting diodes 206 are replaced by other light modulating technologies. However, the row and column addressing circuitry operates in a similar manner.
Referring to FIG. 2, a typical display system includes an external device 220 that produces image data to be displayed. The image data is processed in digital signal processing circuit 222 that produces the control signals and data in a format that is useful to the display device 200.
A number of manufacturers offer driver integrated circuitry for driving flat panel displays, and other integrated circuits for processing digital image pixel data to improve the quality of displayed images. For example, the SED1355 controller offered by Seiko-Epson Corporation (Tokyo, Japan) is a generic controller that produces the proper timing of control signals for flat-panel display devices adhering to the various industry accepted liquid-crystal display and cathode ray tube standards (both digital and analog). Sony Corporation (Tokyo, Japan) manufactures a chip set to perform image processing and driving of its LCDs. The CXD2461 offered by Sony Corporation is a signal processor and timing generator containing various image processing functions such as brightness and contrast correction as well as gamma lookup correction capabilities. Image processing is performed on all pixel data in real time, as is required in video applications. However, for still images, the same pixel data is reprocessed every time the display device is refreshed. This is inefficient in processor usage and requires more complex circuitry and high data rates, consuming more power than necessary. The signal processor and timing generator also outputs various LCD timing signals for designated Sony LCD panels. The CXA2112R offered by Sony Corporation directly drives designated Sony LCD panels via analog signaling. These and other display drivers are physically separate from the display device and require a cable connection to transfer signals from the driver to the display as well as circuit board traces to transfer image data from the image processing circuitry to the driver chip. This has the disadvantages of increased system cost, size, complexity, and added susceptibility to noise. The need for two or more separate devices raises the cost of the system and makes it more complex to design, integrate, manufacture, and use. Often, a separate packaging step is required to integrate the driving device(s) and the display device.
U.S. Pat. No. 5,793,363, issued Aug. 11, 1998 to Takuwa describes a flat panel controller that buffers a frame of an image in a memory external to the display, drives the controller at a first clock frequency, and sends it to the flat panel for display at a second clock frequency.
U.S. Pat. No. 5,737,272 issued Apr. 7, 1998 to Uchiyama et al., discloses a device consisting of a display panel and a circuit substrate that may contain driver electronics mounted on such a display panel. However, the manufacturing process here requires at least three major sub-processing steps:
manufacturing of the display panel, manufacturing of a driver electronics substrate, and the mounting and bonding of the driver electronics substrate on the display panel. This manufacturing process suffers from the inefficiencies of time and added cost for multiple assembly lines. U.S. Pat. No. 6,005,652 issued Dec. 21, 1999, to Matsuhira discloses a liquid crystal display device in which an integrated circuit is incorporated into an LCD panel. Once again, the additional manufacturing step of incorporating the integrated circuit is required to produce the display device.
U.S. Pat. No. 5,258,325 issued Nov. 2, 1993, to Spitzer et al., discloses a display device with digital circuitry on the same substrate. Here, the circuitry is formed on a first substrate, lifted off, and then transferred to a second display substrate. This is a difficult and costly manufacturing step.
Because some active matrix flat panel displays can be fabricated using a process common to that of integrated circuits, there is the opportunity to manufacture such a display containing highly integrated digital circuitry simultaneously. This display simplifies system design and increases system performance because it eliminates costly interconnects, decouples imaging functionality from the main processor, and can run more power efficiently.
U.S. Pat. No. 6,055,034 issued Apr. 25, 2000 to Zhang et al, discloses a xe2x80x9csystem-on-panel,xe2x80x9d where a liquid crystal display panel also contains peripheral driving circuits. These peripheral driving circuits include processor circuitry as well as memory. An earlier patent by Zhang (U.S. Pat. No. 5,995,189, issued Nov. 30, 1999) describes a manufacturing process by which such a xe2x80x9csystem-on-panelxe2x80x9d may be produced.
Sharp-USA (Mahwah, N.J.) also has disclosed a xe2x80x9csystem-on-panelxe2x80x9d concept. Such a device contains both pixel driver and controller circuitry on a common substrate.
Toshiba Corporation (Tokyo, Japan) has announced a liquid crystal display device that contains a single bit of memory located at each pixel site on a semiconductor substrate. This device exhibits the benefits of a self-refreshing display, decreasing system power consumption and improving system cost over more conventional flat panel display technologies. However, any image processing that could help improve the quality of the displayed image must be performed external to the device. This would require either an external processor of increased computational power, or other dedicated integrated circuitry. In either case, the system modularity is decreased, since a display-specific function is performed at a physically different location than the display itself. This could increase system debug time, as well as overall system cost, size, and complexity. The need for extra components or additional processing power elsewhere in the system often increases system power dissipation. Additionally, any extra power consumption implies increased current draw from the voltage sources. In battery-powered systems, the amount of operational time between battery recharges is decreased, making the system less usable and perhaps more expensive to run.
There is a need therefore for an improved method for manufacturing a xe2x80x9csystem-on-panelxe2x80x9d display module to add image processing functionality, so that the image display quality is improved in a manner that also improves system modularity and usability for flat panel display-specific functionality, and lowers system parts counts and external processing requirements.
This need is met according to the present invention by manufacturing a display module, by providing a method of manufacturing a display module, that includes the steps of: providing a substrate; forming on the substrate using the same manufacturing process an image display having an array of addressable display pixels and pixel driver circuitry responsive to control signals and image data for driving the pixels; a digital signal processing circuit having an input interface over which image data and control signals are received; a frame buffer for storing image data and from which image data is read during a display refresh; a display matrix driver circuit for receiving image data from the frame buffer and supplies control signals to the pixel driver circuitry; a control circuit for coordinating storage, retrieval, and display operations, such that the display module is capable of display refresh independently of external control; and an image processing circuit for improving the visual perception of the displayed image.
By including image processing on the common substrate, the current invention has the advantages of increased modularity, reduced complexity, decreased system part count, and a simpler interface between an external image source and the display device.